Essential oils are extremely concentrated botanical substances that have great potential, when used correctly, to support oncology patients. Recent research suggests that certain essential oils may directly address cancer, while others demonstrate synergistic activity with chemotherapy drugs. This article will review and evaluate research literature on Boswellia species (frankincense) for cancer treatment, comparing preparation methods, study designs, and efficacy for cancer treatment. Essential oils, because of their potency, should be taken internally only under the supervision of a trained health-care provider. Thankfully, the oils also are quite effective when inhaled or applied dermally (diluted in a polyunsaturated vegetable oil to a 1%–2% dilution). The scope of this article does not include a discussion of essential oil dosing methods but does review research on maximizing boswellic acid absorption.

Boswellia Species and Cancer TreatmentBoswellia species have been used for centuries to treat cancer in India, North Africa, and the Middle East. Researchers are now designing and conducting in vitro (in a test tube or petri dish) experiments to determine which cancer cell types are responsive to Boswellia. The research also aims to discern which species of Boswellia are most cytotoxic and which plant parts are most effective. In this discussion note variations in several different parameters: Boswellia species, the plant part (resin vs. leaf), and the extraction method (essential oil hydrodistillation vs. solvent extraction methods). These considerations are critical in evaluating the literature so that claims about a particular species or extraction method are not mistakenly attributed to another.

Boswellia SerrataEssential Oil and Boswellic Acids
Many of the most promising studies have focused on boswellic acids, a group of pentacyclic triterpene constituents of Boswellia. Essential oils have a maximum molecular weight of approximately 300 grams per mole (g/mole). In contrast, boswellic acids (both α and β forms) have a molecular weight of 456.7 g/mole.7 Because boswellic acids have a higher molecular weight than an essential oil, essential oils do not contain boswellic acids. Claiming that an essential oil (with a maximum molecular weight of 300) contains boswellic acid (with molecular weight 456) is a physical impossibility.

A 2011 study by Suhail et al. created great excitement (and potentially confusion) about the efficacy of Boswellia essential oil for treating cancer. For this in vitro study, researchers prepared Boswellia sacra essential oil from Omani Hougari-grade resins through hydrodistillation at 78 or 100 °C for 12 hours. Boswellia sacra essential oil-mediated cell viability and death were studied in three established human breast cancer cell lines (T47D, MCF7, MDA-MB-231) and an immortalized normal human breast cell line (MCF10-2A). All three human breast cancer cell lines were sensitive to essential oil treatment with reduced cell viability and elevated cell death.8 The immortalized normal human breast cell line was more resistant to essential oil treatment.

A closer reading of this study, buried on the third page, reveals this important note: "Briefly, a weighed portion of the sample was diluted in methanol, filtered and then analyzed by high performance liquid chromatography. … Boswellic acids were detected by a photodiode array detector."

Personal correspondence with Hsueh-Kung Lin, a lead researcher on the study, confirmed that the sample referred to here was of Boswellia essential oil. Despite the above-mentioned variance in molecular weight, Lin says that boswellic acids may be present in essential oils under two conditions. "First, boswellic acids might be 'coeluted' with other compounds during the 'cooking' process. Second, if a distiller is designed to have a very close distance between water surface and gas phase, high-molecular-weight compounds do not need to travel a long distance and can get into the oil phase." In other words, according to Lin, the boswellic acids likely traveled in water associated with the hydrodistillation process in tandem with the essential oil.

Lin also clarifies, " … even though we detected boswellic acids in our preparations, the content was very low." Lin notes that although much of the research has focused on boswellic acid, "… we believe other compounds or a combination of different compounds can be useful for anticancer activity," a sentiment shared with a group of pharmacological researchers noted below.

Two of the authors of this study are associated with Young Living Essential Oils, a multilevel marketing company whose 2015 annual sales exceeded $1 billion. Young Living Essential Oils certainly has a vested interest in claiming that Boswellia essential oil has anticancer effects. One author, Gary Young, founded the company; another author, Cole Wooley, PhD (doctorate in chemistry, Brigham Young University), was at the time of publication director of research and development at Young Living Essential Oils.

Research studies cited below compare Boswellia essential oil with other methods of extraction.

Anticancer Effects and Increased Sensitivity to Chemotherapy Drugs
An in vitro study examined the effects, of an ethanol extract of the leaves of Boswellia ovalifoliata on triple negative breast cancer cells. Note that this research employed a different species (ovalifoliata instead of serrata), a different extraction method (ethanol instead of essential oil hydrodistillation), and a different plant part (leaves instead of resin). This in vitro study on triple-negative breast cancer cells demonstrated increased apoptosis; decreased NF-κB activation; and increased sensitivity to chemotherapy, specifically doxorubicin and cisplatin. Several studies have confirmed this last effect, of increasing efficacy of chemotherapy agents, with several types of whole essential oils as well as isolated essential oil constituents utilized in the in vitro experiments.9

Another in vitro study utilizing a methanol extract of Boswellia thurifera gum (resin) on human breast cancer cells demonstrated increased p53 activity and cytotoxicity with greater effects at 12 hours than at 6 hours of exposure.10 Note that the study used yet another species (thurifera), a different solvent (methanol), and the gum or resin of the plant. These studies are included here to demonstrate the wide variety of preparation methods, plant parts, and plant species being utilized in Boswellia research.

Research Comparing Preparation Methods and Anticancer Effects
In the last couple of years as Boswellia research has grown more sophisticated, researchers are comparing different preparation methods within the same trial. In a study, published in 2015, researchers made seven different preparations of Boswellia serrata11:

petroleum ether, total extract

methanol extract, total extract

fractions I–IV of methanol extract

essential oil

Each preparation was applied to hepatocellular carcinoma (HCC) and colorectal cancer (CRC) cell lines. The total petroleum and methanol extracts demonstrated the greatest cytotoxicity followed by the methanolic fractions. Although the essential oil did have significant cytotoxic effects on the HCC cell line, it had the least cytotoxicity of the seven preparation methods. The petroleum ether extract's cytotoxic activity exceeded that of doxorubicin (IC50 1.58 and 4.68 respectively). The methanol extract cytotoxicity was comparable to 5-fluorouracil (5-FU).

IC50 (half maximal inhibitory concentration) is a quantitative measure of how much of a particular drug or other substance (inhibitor) is needed to inhibit a given biological process by half. In this case, IC50 measured the concentration needed to kill half of the cancer cells.]

Synergistic Effects of Boswellia and Doxorubicin
Only a handful of essential oil studies have been conducted on humans. The vast majority of the research has been in vitro or animal (murine or rat) studies. The following rat study compared the effects of combining boswellic acid from methanolic extracts with doxorubicin in vitro and in vivo. Both in vitro and in vivo(rat) studies utilized human hepatocellular carcinoma, types HepG2 and Hep3B.12 Combination of doxorubicin and boswellic acid methanolic extracts demonstrated significant (p < 0.001) activity compared with single agent:

increased expression of proapoptotic caspase-3

increased TNF-α activity, dose dependent

decreased antiapoptotic protein NF-ĸB

increased IL-6 activity in cancer cells

decreased SGOT, SGPT, ALP, and bilirubin levels

reversed acute histopathological changes in DOX-treated livers

These last two effects are particularly exciting because liver damage is one of the side effects of doxorubicin that can cause postponement or cancellation of treatments.

Boswellia to Treat Side Effects of Cancer TherapyBoswellia serrata also has therapeutic benefits in addressing side effects of cancer treatment, especially radiation therapies. One study examined the anti-inflammatory effect of Boswellia cream vs. placebo for breast cancer radiation patients.13 The water-based cream contained 2% Bosexil, a lecithin-based phytosome preparation that makes Boswellia serrata more bioavailable. Of 114 subjects, 55 received the 2% Boswellia cream and 59 were given the cream base (placebo). Patients applied the cream twice a day, immediately after radiation treatment and at bedtime; and morning and bedtime on days that they did not have radiation treatment. Erythema was measured by visual grading scale. Fewer patients using the Boswellia cream without concomitant chemotherapy treatment had "intense" erythema (22% in the treated group vs. 49% in the control group). Patients receiving concomitant chemotherapy also had less "intense" erythema rating compared with controls (29% vs. 47%). Patients receiving the Boswellia cream used less corticosteroid creams (25% vs. 63% in the control group).

In a prospective, randomized, placebo-controlled, double-blind pilot study, 44 brain tumor patients receiving radiation therapy were given either 4200 mg/day p.o. Boswellia serrata or placebo.14 The study group had a marked response: 60% of the patients receiving Boswellia had >75% reduction in brain swelling, as measured by MRI. The difference in the amount of dexamethasone between the study and control groups was not statistically significant. Researchers surmised that the findings may be based on an "additional antitumor effect" of Boswellia. There were no severe adverse events in either group. This pilot study offers great hope for the possibility of reducing dexamethasone dosing for brain tumor patients undergoing radiation therapy.

Boswellia and Cancer PreventionBoswellia serrata may help reduce the risk of developing breast cancer for women with dense breast tissue. These women have a significantly increased risk of developing breast cancer compared with women with least dense breast tissue; hence, reducing breast density could in turn reduce breast cancer risk.15,16 In this recent trial of 62 women, the control group of 30 took capsules twice a day containing B2, B6, folic acid, and N-acetylcysteine. The study group took capsules twice a day containing the same nutrients plus boswellic acid, betaine, and myoinositol. In the control group, 22 out of the 30 subjects had extremely dense breast tissue. In the study group, 25 out of 32 were affected by extremely dense breast tissue. At the end of the trial, the control group had no change in breast density. In contrast, the study group had a 60% reduction in breast density as recorded by mammography. Those patients in the study group with decreased tissue compactness also reported reduced breast pain. This study points to the potential role of Boswellia and other supplements to address breast pain and reduce breast density as well as breast cancer risk.